Electrode array assembly and method of making same

ABSTRACT

A lead assembly and a method of making a lead are provided. The method of making a multi-contact lead assembly comprises providing conductive contacts located at an end of a lead body, disposing conductive wires in conductor lumens formed in the lead body, and connecting the conductive wires to the conductive contacts. The method further includes placing spacers between pairs of conductive contacts and inserting monofilament in at least a portion of at least one of the conductor lumens not occupied by the conductor wires. The method also includes reflowing at least one of the spacers or monofilament into at least one portion of at least one of the conductor lumens by heating the spacers and monofilament to a temperature to cause thermal flow or melting of at least one of the spacers or monofilament.

The present application claims the benefit of U.S. Provisional PatentApplication Ser. No. 60/643,093, filed Jan. 11, 2005, which applicationis herein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to implantable leads for providingelectrical stimulation and, more particularly, relates to leads havingmultiple electrode contacts and methods of making such leads.

BACKGROUND

Many types of implantable leads are currently used to treat a variety ofmaladies. Two common treatment applications use leads having multipleelectrode contacts. Cochlear stimulator systems use a multiple electrodecontact lead inserted into one of the cochlear chambers to stimulate thecochlear nerve. Another application where a multiple electrode contactlead is used is the treatment of chronic pain through stimulation of thespinal cord.

Spinal cord stimulation systems generally have two implantablecomponents: an implantable pulse generator (IPG) and at least one leadconnected to one output of the IPG. Generally, however, the IPG is amulti-channel device capable of delivering electrical current throughthe electrode contacts of the lead. The term “lead” used herein willrefer to an elongate device having any conductor or conductors, coveredwith an insulated sheath and having at least one electrode contactattached to the elongate device, usually at the distal portion of theelongate device. The lead can have an inner stylet lumen running throughmost of the length of the lead and which lumen has an opening at theproximal end of the lead. A stylet may be placed into this stylet lumenduring steering and implantation of the lead. The inserted stylet in thelumen can help stiffen the lead so that the stylet/lead combination maybe more easily inserted through tissue.

There are two types of leads that may be used with the IPG. The firsttype is a paddle lead, which has a multiplicity of electrode contactsspread out over a flat, paddle-like surface that is attached to one endof the lead. A paddle lead advantageously permits the electrode contactsto be spaced apart to provide wide coverage over a stimulation area. Adisadvantage presented with a paddle lead is that it usually requires alaminectomy or laminotomy, which are highly invasive surgical proceduresnecessary to implant the large, non-isodiametric paddle.

A second type of lead that is commonly used is a percutaneous lead,which has multiple electrode contacts positioned along the distalportion of an elongate lead. U.S. Pat. No. 6,205,361 issued to Baudinoet al. describes the making of a multi-contact electrode array for alead. The distal end of the lead may be about the same thickness ordiameter as the remainder of the lead. The percutaneous lead isdimensionally configured for tunneling to a target stimulation site. Noinvasive surgical procedure such as a laminotomy is required; thepercutaneous lead may be placed through an epidural type needle reducingsurgical trauma.

The method of making a multi-contact percutaneous lead can be involved.In general, it is desirable to make the lead efficiently, with thefewest number of process steps, maximize the manufacturing yield, andhence reduce the cost of goods of building the leads. There is thus acontinual need to improve the design of a percutaneous lead in order toimprove its performance and to improve the method of manufacturing thelead.

BRIEF SUMMARY

A method of making a lead is provided. In one embodiment of theinvention the method comprises: providing a plurality of conductivecontacts located at the distal end of the stimulation lead; connecting aconductor wire to each of the conductive contacts; placing spacersbetween pairs of adjacent conductive contacts; placing monofilamentwithin void spaces not occupied by a conductor wire, wherein themonofilament is the same material as the spacers; placing a heat shrinktubing around the spacers, conductive contacts and monofilament; andheating the spacers and monofilament just below the melting temperatureto cause thermal fusion between the monofilament and spacer.

The conductive contacts may be connector contacts located at theproximal portion of the lead, which contacts are used to connect to theIPG, or the conductive contacts may be electrode contacts locatedsomewhere on the lead (e.g., usually at the distal end of the lead).

In another embodiment of the method of making the lead, the methodcomprises: providing a plurality of conductive contacts located at theproximal end of the stimulation lead; connecting a conductor wire toeach of the conductive contacts; placing spacers between pairs ofadjacent conductive contacts; placing monofilament within void spacesnot occupied by a conductor wire, wherein the monofilament is adifferent material than the spacers; placing a heat shrink tubing aroundthe spacers, conductive contacts, and monofilament; and heating thespacers and monofilament to a temperature to cause thermal flow ormelting of at least one of the spacers or monofilament.

Hence, while the monofilament and spacers may be the same material withthe same melting temperatures, that is an optional part of theinvention. The monofilament and spacers may actually be differentmaterials, e.g., a type of thermoplastic polyurethane monofilament andanother type thermoplastic polyurethane spacer, with different hardnessand melting points in order to yield a particular stiffness.

In an embodiment of the invention, a lead assembly is providedcomprising: a plurality of electrically conductive contacts; spacersplaced between each adjacent contacts; a conductor wire connected toeach conductive contact; and monofilament placed into void spaces notoccupied by conductor wire, wherein the monofilament is made from thesame insulative material as the spacer; and wherein the spacer andmonofilament are thermally fused from heat applied to the lead assembly,which heat is just below the melting temperature of the spacer and themonofilament material.

In yet another embodiment, a lead assembly is provided comprising: aplurality of electrically conductive contacts; spacers placed betweeneach adjacent contacts; a conductor wire connected to each conductivecontact; and monofilament placed into void spaces not occupied byconductor wire, wherein the monofilament is made from a differentinsulative material as the spacer; and wherein the spacer andmonofilament are heated to a temperature to cause either the spacer ormonofilament material to thermally reflow or melt.

The monofilament and spacer may be the same thermoplastic material tohave the same melting point and to thereby allow thermal fusion uponheating at a temperature just below the melting temperature of thematerial or the monofilament and spacer may have different meltingpoints.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects of the present invention will be moreapparent from the following more particular description thereof,presented in conjunction with the following drawings wherein:

FIG. 1 shows a generalized spinal cord stimulation system with apercutaneous lead connected to an implantable pulse generator (“IPG”);

FIG. 2 shows an illustration of the percutaneous lead implanted into theepidural space of a human spinal cord;

FIG. 3A shows a side view of the distal end of a percutaneous lead.

FIG. 3B shows a side view of the proximal (connector) end of thepercutaneous lead shown in FIG. 3A;

FIG. 4 shows a view of the proximal end of the lead assembly showing theconnector contacts and conductor wires that connect to each connectorcontact;

FIG. 5A shows a cross-sectional view of the percutaneous lead shown inFIG. 3A at line 5A-5A;

FIG. 5B shows a cross-sectional view of the percutaneous lead shown inFIG. 5A along line 5B-5B;

FIG. 5C shows a perspective view of the lead body, having a centralstylet lumen and surrounding smaller lumens for containing conductorwires;

FIG. 6A shows a close-up, partial, longitudinal view of the leadassembly at the distal portion of the lead; and

FIG. 6B depicts how polyurethane monofilament or a thermoplasticmaterial is used to fill the voids and is incorporated into the lead byapplying heat.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

FIG. 1 shows a generalized stimulation system that may be used in spinalcord stimulation (SCS), as well as other stimulation applications. Sucha system typically comprises an implantable pulse generator (“IPG”) 12,an optional lead extension 14, a lead 16 and an electrode array 18. Theelectrode array 18 includes a plurality of electrode contacts 17. In apercutaneous lead, the electrode contacts 17 can be arranged in anin-line electrode array 18 at the distal end of the lead 16. Otherelectrode array configurations can also be used. The IPG 12 generatesstimulation current pulses that are applied to selected electrodecontacts 17 within the electrode array 18.

The proximal end of the lead extension 14 can be removably connected tothe IPG 12 and a distal end of the lead extension 14 can be removablyconnected to a proximal end of the lead 16. The electrode array 18 isformed on a distal end of the lead 16. The in-series combination of thelead extension 14 and lead 16 conduct the stimulation current from theIPG 12 to electrode contacts 17 of the electrode array 18. It is notedthat the lead extension 14 need not always be used with the neuralstimulation system 10. Instead, the lead extension 14 may be used whenthe physical distance between the IPG 12 and the electrode array 18requires its use, or for the purpose of a temporary trial procedure.

The IPG 12 contains electrical circuitry, powered by an internal primary(one-time-use-only) or a rechargeable battery, which through the use ofelectrical circuitry can output current pulses to each stimulationchannel. Communication with the IPG can be accomplished using anexternal programmer (not shown), typically through a radio-frequency(RF) link.

FIG. 2 shows a transverse, mid-sagittal view of a spinal cord and ageneralized, implantable, spinal cord stimulation system. Thestimulation system shown is being used as a spinal cord stimulator (SCS)system. In such an application, the lead 16 and, more particularly, theelectrode array 18 are implanted in the epidural space 20 of a patientin close proximity to the spinal cord 19. Because of the lack of spacenear the lead exit point 15 where the electrode lead 16 exits the spinalcolumn, the IPG 12 may be implanted in the abdomen or above thebuttocks. Use of lead extension 14 facilitates locating the IPG 12 awayfrom the lead exit point 15.

FIG. 3A shows, in accordance with the invention, a distal portion of apercutaneous stimulating lead 16. The stimulating lead 16 is used tostimulate neural tissue by delivering electrical stimulus pulses throughat least one of the electrode contacts 17. The electrode contacts 17 canbe separated by electrode contact spacers (or an insulative material) 61that insulate the electrode contacts 17 from each other. A radiopaquemarker 30 located at the distal tip of the lead 16 may be optionallyincluded. Alternatively, the tip of the lead may be the same material asthe remainder of the lead insulation. The IPG 12 may be configured topermit connection to the two stimulating leads, each having eightelectrode contacts 17. A pair of stimulating leads 16 may be connectedto an IPG 12 and an electrical circuit may be created between oneelectrode contact on the first lead and another electrode contactlocated on the second lead. The IPG 12, for example, may have sixteenindependently programmable outputs that allow programming of pulseamplitude, pulse width and frequency of the pulse width. The electrodecontacts 17 are to be made of a bio-compatible, electrically conductiveelectrode material such as platinum/iridium alloy, platinum, titanium orthe like.

As an example, the stimulating lead 16 may have a diameter of betweenabout 0.03 to 0.07 inches for spinal cord stimulation applications. Aninsertion cannula (not shown), e.g., a 14 gauge insertion needle may beused, while a 0.05 inch diameter stimulating lead is inserted within thecannula to help implant the stimulating lead 16. The stimulating lead 16may come in a variety of lengths, e.g., 30, 50, 70 and 90 cm. Apractitioner can extend the length of any of the available lead lengthsby opting to use an extension lead 14 (shown in FIG. 1). The proximalmale end of the extension lead 14 should be configured to be insertableinto the lead connector of the IPG and the distal female end of theextension lead should be configured to accept the proximal connector endof the stimulating lead 16.

FIG. 3B shows, in accordance with the invention, a depiction of theproximal end of the lead 16. This proximal lead end, including theeight, electrically conductive, connector contacts 40, and a contact tipelement 41, collectively will be called herein as the proximal leadconnector end 42 of the stimulating lead 16. Connector contact spacers45 are placed between the connector contacts 40. The spacers 45 may bemade from an implantable grade polyurethane such as Pellethane® 55Dthermoplastic material. The contacts 40 may be made from anon-corrosive, electrically conductive material, e.g., platinum/iridiumalloy or platinum. Contact tip 41, however, is not electricallyconnected to any conductor and contact tip 41 may merely serve as a hardsurface for a mechanical contact securing device, such as a set screw,which may be used to secure the lead connector end 42 with the connectorblock of the IPG 12. Contact tip 41 is optional and does not need to beincluded as part of the lead. Instead, the contact tip of the lead maybe of similar or the same insulation material as the remainder of thelead 16 or lead body 110 (FIG. 5C).

Preferably the lead 16 is substantially isodiametric, meaning that thediameter along the lead's entire length is equal or nearly equal.However, the lead 16 does not need to be isodiametric. For example, theconnector contacts 40 at the proximal end may be larger (oversized) orsmaller in diameter compared to the remainder of the lead 16 or leadbody 110 (shown in FIG. 5C). Likewise, the electrode contacts 17 may belarger (oversized) or smaller in diameter compared to the remainder ofthe lead 16 or lead body 110 (shown in FIG. 5C).

FIG. 4 shows a proximal lead assembly with each of the connectorcontacts 40 welded to a respective one of conductors 122. Each of theeight connector contacts 40, as shown, are connected to a conductor 122which, in turn, are connected to a respective electrode contact 17 atthe distal end of the stimulating lead 16. The insulating materialbetween the connector contacts 40 and around the conductors 122 is notshown in FIG. 4 for purposes of better illustrating the connectionbetween each conductor and its respective connector contact. Theconnection may be a weld. Cylindrical element 46 is optional and is notconnected to any conductor. Cylindrical element 46 may be used as acontact element for a mechanical securing device such as a set screw inorder to secure the lead 16 to the IPG 12. Alternatively, or inaddition, the cylindrical element 46 may function as a radiopaqueelement, provided that the material used for element 46 is radiopaque.

FIG. 5A shows a cross-sectional view of the lead of FIG. 3A along line5A-5A.

FIG. 5B shows a partial, cross-sectional view of the lead along the line5B-5B.

FIG. 5C shows a perspective view of an exemplary lead body 110 of thelead 16, excluding conductor wires. The lead body is that portion of thelead insulation 112 that is between the distal electrode contact array18 and the array of connectors contacts 40 (FIG. 4) at the proximal leadconnector end 42. The lead body 110 may be extruded as a one-piececomponent. Note the central stylet lumen 114 and the surrounding eightconductor lumens 116.

FIGS. 5A and 5B show an exemplary embodiment of an insulation section112 of the lead body 110 having eight lumens 116 containing theconductor (wires) 122, having individual strands 120. For example 15 or16 individual conductor strands 120 may be braided or bundled into asingle conductor 122. Also shown is a central lumen 114 that may be usedto accept an insertion stylet (not shown) within the lumen to facilitatelead implantation. The opening of the lumen occurs at the proximal endof the lead 16. The lead body 110 may be a biocompatible, insulatinglead material. Preferably the lead body 110 is made from a polyurethane.In particular the material may be Pellethane® thermoplastic material,e.g. 55D, 65D, or other durometer hardness. As previously indicated forFIG. 5C, the lead body 110 shown in FIG. 5B may be extruded as onepiece.

FIG. 6A shows a partial view of a longitudinal, cross-section at thedistal end of the lead, in accordance with an embodiment of theinvention. FIG. 6A shows a ring-like electrode contact 17 (which may beplatinum, for example), multi-stranded conductor 122 and electrodecontact spacer 61 (or an insulative material). The spacer 61, which isring-like in configuration, may be made of polyurethane insulativematerial, e.g., Pellethane®. Monofilament 60, also may be made ofthermoplastic Pellethane® material or other insulation material, e.g.,polyester. During manufacture, the monofilament 60 may be inserted intothe void spaces that are not filled by the conductor 50. A heat shrinktube 65 is also shown placed around the electrode contacts 17 andconductor 122 assembly. The heat shrink tube 65 may be PTFE (e.g.,Teflon® material) or a polyester heat shrink material. The heat shrinktube can be used during manufacturing and is not part of the stimulationlead.

FIG. 6B shows a two-frame, time-elapsed illustration of a partial viewof the distal end of the lead as in FIG. 6A showing the conductor 122connected (e.g., welded) to the electrode contact 17. The first frame(i) of FIG. 6B shows the sequence in which the monofilament 60 fills alarge part of the void space 70. The part of the lead assembly shown isthen placed into a heat, for example, at 190 degrees Celsius for aperiod of 30 seconds. The heat that may be used, e.g., for polyurethanematerial (such as Pellethane®), may range from about 140 to 250 degreesCelsius for a period of about between 15 to 120 seconds. However,importantly, the heat applied to the spacer and monofilament material,should be just below the melting temperature of the material. At thisjust-below-melting temperature, the spacer and monofilament will reflowand thermally fuse together as shown in the second frame (ii). Thespacer 61 and the monofilament 60 may be exactly the same material withthe same melting temperature in order to facilitate thermal fusion. Forexample, the material may be the same implantable grade polyurethanesuch as Pellethane 55D or 75D.

Alternatively, however, the monofilament may be of a different materialthan the spacer to alter the mechanical characteristic of the final leadassembly. The monofilament and spacer may have different melting pointsor very close melting points. The monofilament and spacers may be thesame type of material but with different formulations, e.g., to providedifferent hardness. For example, the monofilament may be a 55D(durometer hardness) material and the spacer may be a 75D material. Thepredetermined temperature chosen to heat both the monofilament andspacers should cause at least one of the materials used to thermallyreflow or, alternatively to melt. In some cases, the temperature may bechosen that one material melts while the other material thermallyreflows.

While FIGS. 6A and 6B show the distal end of the lead, the same processof using a monofilament to fill up void spaces may be used at theproximal end of the lead assembly. At the proximal end of the leadassembly, the conductive contacts are not electrode contacts but, areinstead, electrically conductive connector contacts 40 that must be inelectrical connection with complementary contacts in the IPG connector.The connector contact spacers 45 at the proximal end of the lead (shownin FIG. 3B) are placed between adjacent connector contacts 40. In oneembodiment of the invention, the connector contact spacers 45 may beoversized—that is, the spacers may have an initial diameter that islarger than the final lead diameter. The proximal connector end of thelead assembly 42 may then be heated to a temperature (just below meltingpoint of the spacer and monofilament) for a duration of time previouslydescribed in order to produce thermal fusion of the connector contactspacer 45 and monofilament 60 to create a continuous reflow of materialbetween the spaces not occupied by the connector contacts 40 andconductor wires 122.

Alternatively, the monofilament 60 and spacer 45 may be differentmaterials with different melting points or about the same meltingpoints.

Hence, the method of placing monofilament into void spaces not occupiedby the conductor 122, may be used solely at the distal end of a lead,solely at the proximal end of a lead, or may be employed concurrently atboth ends of a lead. If only one end of a lead employs monofilament, theother end of the lead may employ another method to finish the build,e.g., overmolding using a mold or injecting material such as epoxy,e.g., Hysol® into the void spaces between the contacts and conductorwires.

Example

The following steps illustrates one example embodiment of a method formaking the lead, in accordance with the invention. Embodiments of themethod can include one or more of the following steps (although notnecessarily in the order presented). (1) A braided or bundled,insulated, multi-filament conductor, e.g., having 2-200 filaments, canbe ablated of insulation at one end to expose the conductor. (2) Theexposed end of the conductor can be welded to an electrode contact(located on the distal end lead assembly). (3) Oversized, distal leadspacers may be placed between the electrode contacts. (4) Themulti-lumen tube (lead body) may be pre-cut with ablated section locatedat the distal and proximal ends. (5) Each end of the conductor cable canbe inserted through the corresponding conductor lumens in the lead body.(6) The oversized spacers can be placed between each ring-like electrodecontact at the distal end of the lead assembly; the spacers 61 may be“oversized”, meaning that they may have a diameter greater than the leadbody 110 and in addition, the diameter of the electrode contacts 17 maybe oversized compared to the diameter of the lead body 110. (7) Thedistal end of each conductor cable can be welded to the ring-shapedelectrode contact. (8) Polyurethane monofilament may be placed insidethe void space as shown in FIG. 6A, and inside any empty conductorlumens 116. (9) A heat shrink tube or wrap, preferably, made from PTFE(Teflon) or polyester, can be placed over the distal end of the leadassembly and over the electrode array; this distal end can be placedinto a high temperature block, e.g., between about 140-250 degreesCelsius for a period of about 30 to 120 seconds. (10) The distalassembly can be removed from the heat and the shrink tube or wrap can beremoved. (10) Optionally, the distal tip of the lead can be formed usingan RF welder.

Post processing of the lead is not always required. For example,grinding of the distal or proximal ends of the leads is not necessarywith this method of manufacturing, although optionally, a centerlessgrinding process may be used, if desired.

The method of making the distal and proximal part of the lead, inaccordance with the present invention, eliminates most, if not alltooling, including eliminating the use of molds.

The method of making a lead and the resulting multi-contact lead, inaccordance with the invention, provides advantages over conventionalleads and methods of making a lead. A prior method of making the distalportion of the lead uses epoxy to fill the voids between the spacer 61and the contacts 17. This has certain disadvantages. For instance, useof an epoxy requires a curing step, e.g., of up to eight hours, addingto the total time required to build a lead. With use of epoxy, there mayalso be some variation in stiffness of the final lead assembly post-curebecause the epoxy is generally a different material than the insulativebody or spacers and because curing may occur unevenly. The use of likematerials, e.g., polyurethane lead body, polyurethane spacers andpolyurethane monofilament can yield a better bond between these parts.

Although the lead and method of making the lead are described in thecontext of a spinal cord stimulation lead, it will be understood bythose skilled in the art that the same lead, albeit with appropriatedimensions for a particular application, and the method of making thelead may be used to make a multi-contact lead suitable for use in otherapplications, such as deep brain stimulation, cardiac stimulation andperipheral nerve stimulation.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

1. A method of manufacturing a stimulation lead having a proximal endand a distal end, comprising: providing a plurality of conductivecontacts located at an end of a lead body of the stimulation lead;disposing a plurality of conductor wires in a plurality of conductorlumens formed in the lead body; connecting at least one of the pluralityof conductor wires to each of the conductive contacts; placing spacersbetween pairs of adjacent conductive contacts, wherein portions of theconductor lumens are located beneath the plurality of conductivecontacts and the spacers; inserting monofilament into at least oneportion of at least one of the conductor lumens of the lead body that isnot occupied by the conductor wires; and reflowing at least one of thespacers or monofilament into at least one portion of at least one of theconductor lumens not occupied by the conductive wires by heating thespacers and monofilament to a temperature to cause thermal flow ormelting of at least one of the spacers or monofilament.
 2. The method ofclaim 1, wherein either the spacers or monofilament is polyurethane. 3.The method of claim 2, wherein the monofilament is a thermoplasticmaterial.
 4. The method of claim 3, wherein the heat applied is betweenabout 140 to 250 degrees Celsius.
 5. The method of claim 4, wherein theheat is applied for between about 15 to 120 seconds.
 6. The method ofclaim 1, wherein the spacers are oversized in diameter, relative to apredetermined final diameter of the lead.
 7. The method of claim 1,wherein conductive contacts are in the form of rings.
 8. The method ofclaim 1, wherein the conductive contacts are electrode contacts on thelead.
 9. The method of claim 1, wherein the conductive contacts areconnector contacts on the proximal end of the lead.
 10. The method ofclaim 1, wherein the step of connecting a conductor wire to each of theelectrode contacts is accomplished by welding each conductor wire toeach respective contact.
 11. The method of claim 1, wherein themonofilament is a different material than the spacers.
 12. The method ofclaim 1, wherein the monofilament is the same material as the spacers.13. The method of claim 5, wherein the heat applied is about 160 degreesCelsius for about 40 seconds.
 14. The method of claim 1, wherein theplurality of electrically conductive contacts are located on theproximal end of the stimulation lead.
 15. The method of claim 1, whereinthe plurality of electrically conductive contacts are located on thedistal end of the stimulation lead.
 16. The method of claim 1, whereinthe plurality of electrically conductive contacts and the spacers form asubstantially cylindrical body and wherein the conductor lumens aredefined within the substantially cylindrical body.
 17. The method ofclaim 1, wherein the monofilament is disposed in an orientation parallelto the conductor wires.
 18. The method of claim 1, further comprisingplacing a heat shrink tubing around the spacers, conductive contacts,and monofilament and removing the heat shrink tubing after reflowing atleast one of the spacers or monofilament.
 19. The method of claim 18,wherein the heat shrink tubing is made from a material selected from thegroup consisting of PTFE or polyester heat shrink material.